2025-08-18
(1) Traveling wave method: When an electric wave is transmitted in a transmission line, if the transmission line is uneven, that is, the characteristic impedance of a certain point in the transmission line changes, when the electric wave reaches this point, in addition to continuing to transmit farther, it will also transmit in the opposite direction and return to the test end. We call this reversely transmitted electric wave a reflected wave. The phenomenon of electric waves transmitting in the opposite direction is called the reflection phenomenon of electric waves. The so-called traveling wave refers to the general term for incident waves and reflected waves.
(2) When an electric wave is transmitted in a transmission line, the polarity of the echo at the short-circuit point is opposite to the polarity of the transmitted pulse, while the polarity of the echo at the break point (including the cable terminal) is the same as the polarity of the transmitted pulse. For general low-resistance and open-circuit faults, the low-voltage pulse method can be used to easily determine the distance between the fault point and the test end based on the polarity of the echo.
(3) For high-resistance faults, we use the high-voltage flashover method to test. For leaky high-resistance faults, we use a high-voltage pulse signal source to cause the cable fault point to flash over and discharge, causing the fault point to generate a reflection signal, and the fault reflection wave is detected at the test end. For flashover high-resistance faults, we use a DC high-voltage power supply to cause the cable fault point to flash over and discharge, causing the fault point to generate a reflection signal, and the fault reflection wave is detected at the test end.
(4) Signal processing process of the cable fault tester: The signal applied to the cable generates a reflection signal after encountering the fault point. The reflection signal is given to the input circuit. These two signals pass through the high-speed A/D converter and computer control system in succession, converting the analog signal into a digital signal, storing it, and performing digital processing. The test waveform is then displayed on the display for waveform analysis, completing the rough measurement of the fault distance.
